In the given figure, AB and CD are diameters of a circle with centre O perpendicular to each other. If OA =7 cm, find the area of shaded region.

Area of quadrant \(\displaystyle \mathrm{BOC}=\frac{1}{4} \times \frac{22}{7} \times 7 \times 7\) \[=\frac{77}{2} \mathrm{~cm}^{2} \] Area of \(\displaystyle \Delta \mathrm{BOC}=\frac{1}{2} \times \mathrm{OB} \times \mathrm{OC}=\frac{1}{2} \times 7 \times 7\) \[=\frac{49}{2} \mathrm{~cm}^{2} \] Area of shaded region \(\displaystyle =2\left[\frac{77}{2}-\frac{49}{2}\right]=28 \mathrm{~cm}^{2}\)